Link state routing techniques

ABSTRACT

A link state routing communication device allowing path precalculation satisfying the required quality of a connection and reducing the call blocking probability is disclosed. A path satisfying a connection request can be selected from a plurality of precalculated paths which are stored for each destination in a memory. The precalculated paths reflect the latest link resource information using the feasibility check operation or precalculated path update operation. Therefore, a blocking probability of connection setup using precalculated paths can be decreased. In a border node, summarized information is calculated based on precalculated paths and therefore high-speed summarized information calculation is allowed, resulting in reduced computation load.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to link state routing techniques in anetwork which is structured into single-level or multi-level hierarchy,and in particular to a link state routing device and method fordetermining an optimal path using topology information andquality-of-service (QoS) information of the entire network, which areobtained by exchanging route information including link or nodaltopology information and QoS information between single peer group nodesor hierarchical peer group nodes in the network.

2. Description of the Related Art

A QoS routing algorithm for finding a path that guarantees QoSparameters requested by users has been proposed by IWATA et al. “ATMRouting Algorithms with Multiple QOS Requirements for MultimediaInternetworking” (IEICE Transactions on Communications, Vol. E79-B. No.8. pp 999–1007. August 1996).

More specifically, the QoS routing algorithm includes a precalculatedpath approach and an on-demand calculated path approach. When receivinga connection setup request from a user, the precalculated path approachis performed to search a precalculated path resource information memoryfor a candidate path satisfying the QoS requirement of the connectionsetup request. If such a candidate path is found, then the connection isset up. Contrarily, when not found, the connection setup request issupplied to the on-demand calculated path approach.

The on-demand calculated path approach calculates a path satisfying theQoS requirement of the connection setup request based on link resourceinformation stored in a link resource information memory. When such apath is found, then the connection is set up. Contrarily, when notfound, the connection setup request is finally rejected.

The link resource information memory stores link resource informationsuch as available bandwidth and delay for each link. When receiving linkresource information from another node, it is determined whether anychange in link resource information occurs in the link resourceinformation memory. If any link resource information is changed, thenthe corresponding link resource information is updated.

In the case of a large hierarchical network, a border communicationdevice is needed to exchange summarized link resource informationbetween different-level nodes. Such a border communication device forlink state routing has been proposed by Korkmaz et al. “Source-OrientedTopology Aggregation with Multiple QoS parameters in Hierarchical ATMNetworks” (IEEE/IFIP IWQoS'99, pp. 137–146, June 1999).

More specifically, such a border communication device is provided with asummarized information computation means. When the contents of a linkresource information memory has been updated, the summarized informationcomputation means summarizes network status of nodes in its own levelwhile referring to the updated contents of the link resource informationmemory. The summarized information is sent to another level of thehierarchy.

There have been proposed various communication devices similar to theabove communication devices. For example, Japanese Patent No. 2723097discloses a QoS routing device capable of selecting a path satisfyingall the QoS requirements of a connection setup request. Japanese PatentApplication unexamined Publication No. 11-252106 discloses a connectionpath changing device capable of re-establishing a connection so as toget around a designated node after connection establishment. JapanesePatent Application Unexamined Publication No. 10-164074 discloses an ATMnetwork system capable of searching for a connection path satisfying QoSwhen routing in the network and also reducing the load of connectionsetup. Japanese Patent Application Unexamined Publication No. 10-135980discloses a connection setup device avoiding causing an establishedconnection to degrade the quality thereof and allowing rapid recovery ofthe connection. Japanese Patent Application Unexamined Publication No.10-154979 discloses a point-to-multipoint connection method for settingup a point-to-multipoint call by selecting an economical connection pathin a broad-band communications network.

A combination of path precalculation and dynamic route search employedin the conventional link-state routing devices as described above hasdisadvantages that there is often the case where a precalculated pathsatisfying the connection quality requirement is not found. The reasonis that only a single precalculated path is used for each destination,resulting in a few candidate paths. This increases the number of times apath is dynamically calculated and thereby increases the load.

In addition, since the precalculated path information fails to reflectthe latest path information, there is a high probability of connectionsetup failure.

As for the border communication device as described above, calculationof summarized information needs the high computing power because it isnecessary to search the entire network of its own and repeatedly performcalculation with accuracy.

Further, the summarized information is sent to another level of thehierarchy every time when the network status of its own is updated.Therefore, the amount of packet data is increased, which may causenetwork congestion.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a link state routingcommunication device allowing path precalculation satisfying therequired quality of a connection and reducing the call blockingprobability.

Another object of the present invention is to provide a link staterouting communication device allowing summarized information to becalculated at high speed and with reduced computation load.

Still another object of the present invention is to provide a link staterouting communication device allowing the reduced amount of summarizedinformation sent to the network.

According to the present invention, a link state routing device of anode in a network composed of a plurality of nodes and links, includes:a first memory for storing link resource information for each link inthe network, wherein the link resource information is updated asoccasion arises; a path calculator for calculating a plurality ofprecalculated paths for each destination based on link resourceinformation stored in the first memory, independently of occurrence of aconnection request; a second memory for storing the precalculated pathsfor each destination and path resource information for eachprecalculated path; and a path selector for selecting a precalculatedpath from the precalculated paths stored in the second memory when aconnection request occurs, wherein the precalculated path is selected soas to satisfy quality requirement of the connection request.

The path selector may include: a precalculated path searcher forsearching the second memory for a precalculated path candidatesatisfying quality requirement of the connection request; and afeasibility checker for checking whether the precalculated pathcandidate is a feasible path, by referring to link resource informationstored in the first memory, wherein, when the precalculated pathcandidate is an infeasible path, the precalculated path searchersearches the second memory for another precalculated path candidate.

The path selector may further include: an on-demand path searcher forsearching the first memory for a path candidate satisfying qualityrequirement of the connection request received, wherein, when aprecalculated path candidate satisfying quality requirement of theconnection request received is not found, the on-demand path searcher isactivated.

The link state routing device may further include: an updater forupdating path resource information of a precalculated path stored in thesecond memory when link resource information of a link included in theprecalculated path is updated.

According to another aspect of the present invention, a link staterouting device of a node in a network composed of a plurality of nodesand links, includes: a first memory for storing link resourceinformation for each link in the network, wherein the link resourceinformation is updated as occasion arises; a path calculator forcalculating a plurality of precalculated paths for each destinationbased on link resource information stored in the first memory,independently of occurrence of a connection request; a second memory forstoring the precalculated paths for each destination and path resourceinformation for each precalculated path; a path selector for selecting aprecalculated path from the precalculated paths stored in the secondmemory when a connection request occurs, wherein the precalculated pathis selected so as to satisfy quality requirement of the connectionrequest; a connection setup attempter for attempting connection setup ofthe precalculated path; a first counter for counting number of pathselection occurrences in the path selector; a second counter forcounting number of path blocking occurrences in the connection setupattempter; a blocking rate calculator for calculating a blocking ratebased on the number of path selection occurrences and the path blockingoccurrences; and a controller controlling the path calculator such that,when the blocking rate is not smaller than a predetermined threshold,the path calculator recalculates a plurality of precalculated paths foreach destination based on link resource information stored in the firstmemory.

The path selector may include: a precalculated path searcher forsearching the second memory for a precalculated path candidatesatisfying quality requirement of the connection request; and afeasibility checker for checking whether the precalculated pathcandidate is a feasible path, by referring link resource informationstored in the first memory, wherein, when the precalculated pathcandidate is an infeasible path, the precalculated path searchersearches the second memory for another precalculated path candidate.

According to still another aspect of the present invention, a link staterouting device of a node in a network composed of a plurality of nodesand links, includes: a first memory for storing link resourceinformation for each link in the network, wherein the link resourceinformation is updated as occasion arises; a path calculator forcalculating a plurality of precalculated paths for each destinationbased on link resource information stored in the first memory,independently of occurrence of a connection request; a second memory forstoring the precalculated paths for each destination and path resourceinformation for each precalculated path; a path selector for selecting aprecalculated path from the precalculated paths stored in the secondmemory when a connection request occurs, wherein the precalculated pathis selected so as to satisfy quality requirement of the connectionrequest; an updater for updating path resource information of aprecalculated path stored in the second memory when link resourceinformation of a link included in the precalculated path is updated; anda controller controlling the path calculator such that, when the updatedlink resource information of the link is not smaller than apredetermined link quality threshold, the path calculator recalculates aplurality of precalculated paths for each destination exclusive of theupdated link resource information of the link.

A communication device of a border node for link state routing inhierarchical networks, includes: a first memory for storing linkresource information for each link in the network, wherein the linkresource information is updated as occasion arises; a path calculatorfor calculating a plurality of precalculated paths for each destinationbased on link resource information stored in the first memory,independently of occurrence of a connection request; a second memory forstoring the precalculated paths for each destination and path resourceinformation for each precalculated path, and a summarized informationcalculator for calculating summarized information from the precalculatedpaths for each destination and path resource information for eachprecalculated path.

The summarized information calculator may include: an update linkdetector for detecting a precalculated path including an updated link,wherein the summarized information calculator recalculates onlysummarized information of a precalculated path including the updatedlink.

A communication device of a border node for link state routing inhierarchical networks, includes: a first memory for storing linkresource information for each link in the network, wherein the linkresource information is updated as occasion arises; a summarizedinformation calculator for calculating summarized information based onthe link resource information for each link stored in the first memory;a change rate calculator for calculating a change rate between new linkresource information currently received from another node and the linkresource information stored in the first memory, that was previouslysent to a different-level node; and a summarized information transmitterfor transmitting the summarized information to a different-level nodewhen a calculated change rate is greater than a predetermined threshold.

As described above, according to the present invention, a pathsatisfying a connection request can be selected from a plurality ofprecalculated paths which are stored for each destination. Therefore, ahigh-speed connection setup can be achieved without re-calculating apath when a connection request occurs.

Since the precalculated paths reflect the latest link resourceinformation using the feasibility check section or precalculated pathupdate section, a blocking probability of connection setup usingprecalculated paths can be decreased.

In a border node, summarized information is calculated based onprecalculated paths and therefore high-speed summarized informationcalculation is allowed, resulting in reduced computation load.

In addition, calculation and transmission of summarized information arecontrolled depending on a change rate of summarized information.Therefore, the amount of summarized information transferred in thenetwork can be reduced and a sequence of processes regarding receptionof summarized information at different-level nodes can be omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a link state routing communicationdevice according to a first embodiment of the present invention;

FIG. 2 is a flow chart showing an operation of the first embodiment;

FIG. 3A is a diagram showing an example of possible network routes forexplanation of an operation of the first embodiment;

FIGS. 3B–3E are diagrams showing precalculated paths for explanation ofthe first embodiment;

FIG. 3F is a diagram showing a link resource information table forexplanation of the first embodiment;

FIG. 3G is a diagram showing a precalculated path information table forexplanation of the first embodiment;

FIG. 4 is a block diagram showing a link state routing communicationdevice according to a second embodiment of the present invention;

FIG. 5 is a flow chart showing an operation of the second embodiment;

FIG. 6A is a diagram showing a precalculated path information table forexplanation of an operation of the second embodiment;

FIG. 6B is a diagram showing a change of resource information forexplanation of an operation of the second embodiment;

FIG. 6C is a diagram showing an updated precalculated path informationtable for explanation of an operation of the second embodiment;

FIG. 7 is a diagram showing a precalculated path table used in ahierarchically weighted round robin scheme;

FIG. 8 is a block diagram showing a link state routing communicationdevice according to a third embodiment of the present invention;

FIG. 9 is a flow chart showing an operation of the third embodiment;

FIG. 10 is a block diagram showing a link state routing communicationdevice according to a fourth embodiment of the present invention;

FIG. 11 is a flow chart showing an operation of the fourth embodiment;

FIG. 12 is a block diagram showing a link state routing bordercommunication device according to a fifth embodiment of the presentinvention;

FIG. 13A is a diagram showing an example of possible network routes forexplanation of the fifth embodiment;

FIG. 13B is a diagram showing summarized links for explanation of thefifth embodiment;

FIG. 14A is a diagram showing an example of possible network routes forexplanation of an operation of the fifth embodiment;

FIGS. 14B–14E are diagrams showing precalculated paths for explanationof the fifth embodiment;

FIG. 14F is a diagram showing a link resource information table forexplanation of the fifth embodiment;

FIG. 14G is a diagram showing a precalculated path information table forexplanation of the fifth embodiment;

FIG. 15 is a diagram showing a summarized link resource informationtable for explanation of the fifth embodiment;

FIG. 16 is a block diagram showing a link state routing communicationdevice according to a further embodiment of the present invention;

FIG. 17 is a flow chart showing an operation of the further embodiment;

FIG. 18A is a diagram showing a table containing link resourceinformation of the link a-e in the level for explanation of an operationof the further embodiment;

FIG. 18B is a diagram showing a table containing information about afirst precalculated path from node 501 to node 503 and a secondprecalculated path from node 501 to node 505 in operation of the furtherembodiment; and

FIG. 18C is a diagram showing a table containing summarized informationof the level for explanation of an operation of the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, link state routing communication devices and link staterouting border communication devices will be described in detail.

First Embodiment

A link state routing communication device according to a firstembodiment of the present invention is designed to be used in a singlepeer group.

Referring to FIG. 1, the link state routing communication device isprovided with a link resource information receiver 1, a data processor2, a memory device 3, a connection request receiver 4, and a connectionsetup section 5. The link resource information receiver 1 receives linkresource information from another communication device and outputs it tothe data processor 2. The connection request receiver 4 receives aconnection request including the destination and required connectionquality of a call from a user and outputs it to the data processor 2.The data processor 2 performs a link state routing operation using thememory device 3 when receiving a connection request from the connectionrequest receiver 4. The connection setup section 5 sets up a connectionto the destination of the received connection request under control ofthe data processor 2.

The data processor 2 is a program-controlled processor on which thefollowing sections are implemented: link resource information updatesection 21, plural-path precalculation section 22, and a path searcher23 including precalculated path searcher 231, on-demand path searcher232; and feasibility check section 233. The memory device 3 includeslink resource information memory 31 and precalculated path memory 32including precalculated path topology memory 321 and precalculated pathresource information memory 322.

The link resource information memory 31 stores link resource informationreceived from another communication device in the network. Link resourceinformation may be available bandwidth and delay information on a link.

The precalculated path topology memory 321 stores as path topology acollection of node and links on a precalculated path to a destination.

The precalculated path resource information memory 322 stores pathresource information corresponding to each path topology stored in theprecalculated path topology memory 321. Taking an available bandwidth ona path as an example of path resource, the path resource informationindicates a minimum available bandwidth among the links on the path. Thepath resource information stored in the precalculated path resourceinformation memory 322 is updated when the link resource informationstored in the link resource information memory 31 is updated.Alternatively, it is periodically updated independently of the linkresource information stored in the link resource information memory 31.

The link resource information update section 21 updates the linkresource information stored in the link resource information memory 31when a change of corresponding link resource information is detected bycomparing the received link resource information from the link resourceinformation receiver 1 with the stored link resource information in thelink resource information memory 31.

The plural-path precalculation section 22 calculates a plurality ofpaths from its own device to the destination of the received connectionrequest before accepting the connection request. The precalculation isperformed using the link resource information stored in the linkresource information memory 31. The path topology information and theresource information of each of the precalculated paths are registeredinto the precalculated path topology memory 321 and the precalculatedpath resource information memory 322, respectively. Since a plurality ofprecalculated paths are registered, it is possible to rapidly find anoptimal precalculated path satisfying QoS requirements of the receivedconnection request, resulting in the decreased number of times a path isdynamically re-calculated.

The precalculated path searcher 231, when receiving a connectionrequest, searches the precalculated path resource information memory 322for a precalculated path candidate satisfying the QoS requirements usingthe destination and the connection quality of the received connectionrequest as a search key.

The feasibility check section 233 checks whether each link oil the foundprecalculated path satisfies the required connection quality byreferring to the stored link resource information in the link resourceinformation memory 31. As described before, the precalculated pathsstored in the precalculated path memory 32 do not always reflect thelatest link resource status. Therefore, if only the precalculated pathsstored in the precalculated path memory 32 are used to set up aconnection, a call blocking probability becomes high. According to thefirst embodiment, the feasibility check section 233 is used to determinewhether each line on the found precalculated path satisfies the requiredconnection quality, resulting in substantially reduced call blockingprobability.

The on-demand path searcher 232 calculates a path satisfying therequired connection quality of the received connection request based onthe link resource information stored in the link resource informationmemory 31.

Operation

Next, a link state routing operation according to the first embodimentwill be described with reference to FIG. 2.

Referring to FIG. 2, when receiving a connection request (step A1), theprecalculated path searcher 231 searches the precalculated path topologymemory 321 for a precalculated path to the destination of the receivedconnection request. Thereafter, the precalculated path searcher 231searches the precalculated path resource information memory 322 for aprecalculated path candidate satisfying the required connection qualityusing the destination and the connection quality of the receivedconnection request as a search key (step A2).

When no candidate is found (NO at step A3), the on-demand path searcher232 calculates an on-demand path satisfying the required connectionquality of the received connection request based on the link resourceinformation stored in the link resource information memory 31 (step A5).When such an on-demand path is found (YES at step A6), it is output tothe connection setup section 5 and the connection is set up (step A4).When such an on-demand path is not found (NO at step A6), the connectionis blocked (step A7).

On the other hand, when a precalculated path candidate satisfying therequired connection quality is found (YES at step A3), it is output tothe feasibility check section 233. The feasibility check section 233checks whether each link on the found path candidate satisfies therequired connection quality by referring to the stored link resourceinformation in the link resource information memory 31 (step C1). Whenthe found path candidate satisfies the required connection quality (YESat step C1), it is output to the connection setup section 5 and theconnection is set up (step A4). When the found path candidate does notsatisfy the required connection quality (NO at step C1), control goesback to the step A2 so as to select another precalculated pathcandidate.

EXAMPLE

As shown in FIGS. 3A–3E, it is assumed for simplicity that a single peergroup consists of five nodes 501–505 (see FIG. 3A) and fourprecalculated paths 521–524 from the node 501 to the node 503 areconsidered (see FIGS. 3B–3E).

In this case, the link resource information memory 31 of the node 501stores a link resource information table 511 as shown in FIG. 3F and theprecalculated path memory 32 thereof stores a precalculated pathinformation table 531 as shown in FIG. 3G. Referring to FIG. 3F, a linka-b, for example, has a delay of 3 msec and an available bandwidth (BW)of 30 Mbps. Referring to FIG. 3G, a precalculated path a-b-c, forexample, is shown to have a delay of 7 msec and an available bandwidthof 80 Mbps.

The plural-path precalculation section 22 periodically updates theprecalculated path information table 531 by referring to the linkresource information table 511.

Assuming that the connection request receiver 4 receives a connectionrequest for a connection to the node 503 of BW=50 Mbps and delay≦8 msec,the precalculated path searcher 231 searches the precalculated pathinformation table 531 for a precalculated path satisfying the connectionrequest. In this case, the precalculated path searcher 231 finds theprecalculated path 521, that is, a-b-c, which is indicated to have abandwidth of 80 Mbps and a delay of 7 msec (see FIG. 3G).

As described before, the contents of the precalculated path informationtable 531 are updated at regular intervals. Therefore, when theprecalculated path searcher 231 accesses the precalculated pathinformation table 531, there is a possibility that the precalculatedpath information has not reflected the latest network status. To avoidthis, the feasibility check section 233 checks whether each line on theprecalculated path 521 satisfies the required connection quality.

More specifically, the precalculated path 521 consists of two links a-band b-c as shown in FIG. 3B. Referring to the link resource informationtable 511 of FIG. 3F, the link a-b has 30 Mbps, which does not satisfythe required bandwidth of 50 Mbps (NO at step C1 of FIG. 2).Accordingly, the feasibility check section 233 instructs theprecalculated path searcher 231 to select another precalculated pathcandidate.

Referring to FIG. 3F, the precalculated path searcher 231 selects as anext candidate the precalculated path 522: a-c. Referring to the linkresource information table 511 of FIG. 3F, the link a-c is shown to havea bandwidth of 60 Mbps and a delay of 3 msec, which satisfies therequirements of BW=50 Mbps and delay≦8 msec (YES at step C1 of FIG. 2).Accordingly, the feasibility check section 233 determines that theprecalculated path 522 is feasible. Then, the precalculated path 522 isoutput to the connection setup section 5 and the connection followingthe precalculated path 522 is set up.

As described above, the plural-path precalculation section 22 registersa plurality of precalculated paths in the precalculated path memory 32.Therefore, it is possible to rapidly find an optimal precalculated pathsatisfying QoS requirements of the received connection request withhigher probability, resulting in the decreased number of times a path isdynamically re-calculated and thereby reduced computation load on thecommunication device.

Further, the feasibility check section 233 uses the latest link resourceinformation table to determine whether each line on the foundprecalculated path satisfies the required connection quality. Therefore,a probability of successfully setting up a connection becomes higher,resulting in reduced call blocking probability.

Second Embodiment

A link state routing communication device according to a secondembodiment of the present invention is designed to be used in a singlepeer group.

Referring to FIG. 4, the link state routing communication device isprovided with a link resource information receiver 1, a data processor10, a memory device 11, a connection request receiver 4, and aconnection setup section 5, wherein circuit blocks similar to thosepreviously described with reference to FIG. 1 are denoted by the samereference numerals, and the descriptions thereof will be omittedhereinafter.

The data processor 10 is a program-controlled processor on which thefollowing sections are implemented: link resource information updatesection 21; plural-path precalculation section 22; path searcher 24including precalculated path searcher 231 and on-demand path searcher232; and precalculated path resource information searcher 25. The memorydevice 11 includes link resource information memory 31 and precalculatedpath memory 33 including precalculated path topology memory 321,precalculated path resource information memory 322, and link-pathcorrespondence table 323.

The link-path correspondence table 323 indicates which of precalculatedpaths each link is included in.

The precalculated path resource information searcher 25 receives updatelink information from the link resource information update section 21and uses the update link information as a search key to search thelink-path correspondence table 323 for a corresponding precalculatedpath. Thereafter, the precalculated path resource information searcher25 searches the link resource information memory 31 for link resourceinformation of the corresponding precalculated path and, if found, thenupdates the path resource information stored in the precalculated pathresource information memory 322. Accordingly, the link resourceinformation is updated and, at the same time, the path resourceinformation of the corresponding precalculated path is also updated.

Operation

Referring to FIG. 5, when receiving link resource information fromanother node (step B0), the link resource information update section 21identifies a link on which a change of resource information occurs (stepB1) and updates corresponding link resource information stored in thelink resource information memory 31 (step B2).

In addition, the precalculated path resource information searcher 25uses the changed link information as a search key to search thelink-path correspondence table 323 for a corresponding precalculatedpath (step F1). Thereafter, the precalculated path resource informationsearcher 25 searches the link resource information memory 31 forresource information of the corresponding precalculated path and updatesthe path resource information stored in the precalculated path resourceinformation memory 322 (step F2). The step F2 is repeatedly performeduntil path resource information of all precalculated paths including theupdated link have been updated (step F3).

EXAMPLE

It is here assumed that the link resource of a link a-c is changed.

As shown in FIG. 6A, the precalculated path memory 33 stores aprecalculated path information table 541 which includes precalculatedpath topology information, precalculated path resource information, andlink-path correspondence information. In this case, precalculated pathinformation including the link a-c is shown in FIG. 6A.

When the link resource information update section 21 detects a change ofresource information of the link a-c as shown in FIG. 6B, theprecalculated path resource information searcher 25 updates theprecalculated path information table 541 to a table 542 as shown in FIG.6C.

Concretely, as shown in a table 551 of FIG. 6B, the delay time of thelink a-c increases by 2 msec from 3 msec to 5 msec. Since delay orjitter is an additive parameter, the precalculated path resourceinformation searcher 25 increases all delays of precalculated pathsassociated with the changed link a-c across the board by 2 msec (see“delay” column of the table 542 as shown in FIG. 6C).

On the other hand, the available bandwidth of the link a-c decreasesfrom 60 Mbps to 40 Mbps. Since a bandwidth is a non-additive parameter,only available bandwidths of precalculated paths greater than 40 Mbps inthe table 541 are uniformly decreased to 40 Mbps (see “BW” column of thetable 542 as shown in FIG. 6C). In other words, the available bandwidthof a precalculated path is determined by the minimum bandwidth among thelinks included in the precalculated path. Therefore, in FIG. 6C, onlythe precalculated path a-c-e is not changed in available bandwidthbecause its original available bandwidth is 30 Mbps, smaller than 40Mbps.

In the case where the available bandwidth increases, it is necessary tore-calculate path resource information by referring to the link resourceinformation of each link included in a precalculated path in question.

As described above, according to the second embodiment, when the linkresource information is updated, the path resource information of thecorresponding precalculated paths is also updated without using theplural-path precalculation section 22. Accordingly, precalculated pathselection can be performed based on the latest path resource informationwithout the feasibility check section that is needed in the firstembodiment, resulting in reduced load of computation and decreased callblocking probability.

In the first and second embodiments, the plural-path precalculationsection 22 may perform precalculation based on link-inherent parametersthat are independent of link resource information, such asAdministrative Weight and propagation delay. In the case whereparameters dependent on the above link resource information such asavailable bandwidth and delay are used to perform path precalculation,it is necessary to perform the precalculation every time link resourceinformation is changed, resulting in increased load of computation.Therefore, using link-inherent parameters allows reduced computationload.

The plural-path precalculation section 22 may perform precalculation aplurality of times based on a single parameter. For example, for adestination, a path having minimum number of hops, a path having maximumavailable bandwidth, and a path having minimum delay time are previouslycalculated and stored. In this case, a path precalculation unit that wasdesigned for a conventional communication device can be also used in thepresent invention, resulting in reduced time required for design.

The plural-path precalculation section 22 may perform precalculationbased on an integrated parameter having a plurality of parametersincluding available bandwidth and delay integrated in certainproportions. For example, such an integrated parameter may be obtainedby adding 1000/delay[msec] to available bandwidth[Mbps]. In this case,by performing precalculation only once, precalculated paths reflecting aplurality of parameters can be obtained, resulting in reducedcomputation load.

Path Selection Control

How to select a path to be used for connection setup affects efficientuse of network resources, For example, among paths all satisfying thesame quality requirement, one having smaller number of hops is selectedto suppress resource consumption of a link, achieving efficient networkutilization.

By controlling the precalculated path searcher 231, it is possible tochange selecting order of a path to be used for connection setup.Several examples will be described hereafter.

Integrated Parameter

In the precalculated path searcher 231, precalculated paths arepreviously sorted according to a certain integrated parameter. When aconnection request occurs, the precalculated path searcher 231sequentially checks the sorted precalculated paths to find aprecalculated path candidate satisfying the connection request.

Taking the case of FIGS. 3A–3G as an example, when an availablebandwidth is used as an integrated parameter, the searching order of theprecalculated paths 521–524 is as follows: 521, 522, 524, and 523.

In the case where a value obtained by 1000/delay[msec]+availablebandwidth [Mbps] is used as an integrated parameter, the respectiveintegrated parameter values of the precalculated paths 521–524 are 222,393, 530, and 216. Therefore, if these integrated parameters are sortedin descending order, then the searching order of the precalculated paths521–524 is as follows: 523, 522, 521, and 524.

As describe above, by changing the integrated parameter, selecting orderof a path candidate to be used for connection setup can be controlled,allowing the efficient utilization of network resources to be adjusted.

Weighted Round Robin

Alternatively, a precalculated path candidate to be used for connectionsetup may be selected in a weighted round robin fashion using anintegrated parameter as a weight.

In the case where a precalculated path candidate satisfying theconnection request is selected from the previously sorted precalculatedpaths as described before, the leading one in the previously sortedprecalculated paths is used for connection setup with high probability,resulting in uneven using frequency. By using the weighted round robinscheme, using frequency is uniformly distributed among precalculatedpaths using the same integrated parameter.

Hierarchically Weighted Round Robin

A precalculated path candidate to be used for connection setup may beselected in a hierarchically weighted round robin fashion.

In FIG. 7, nine precalculated paths a to i to the same destination, eachsatisfying connection quality requirements, are shown as an example. Afirst group of precalculated paths a, b, and c needs three hops to thedestination, a second group of precalculated paths d, e, and f needsfour hops to the destination, and a third group of precalculated pathsg, h, and needs five hops to the destination. The available bandwidth ofeach precalculated path is currently determined as shown in “availableBW” column of FIG. 7.

Here, the number of hops is used as the first weight in thehierarchically weighted round robin and the available bandwidth is usedas the second weight.

First, group selection is performed according to the first weight(number of hops). In this example, the first, second, and third groupsare selected in proportions of 3:4:5 each corresponding to the numbersof hops thereof, respectively.

Second, in a selected group, path selection is performed according tothe second weight (available bandwidth). For example, in the case of thefirst group (three hops) being selected, the precalculated paths a, b,and c are selected in proportions of 100:50:10 each corresponding to theavailable bandwidths thereof, respectively.

It is possible to designate a weight on which the round robin selectionis not performed. For example, the first weight (number of hops) is notused to perform the round robin selection but to just sort theprecalculated paths. In this example, a precalculated path having thesmaller number of hops can be always selected.

As describe above, by changing a hierarchical weight, selecting order ofa path candidate to be used for connection setup can be controlled,allowing the efficient utilization of network resources to be adjusted.Further, by using the hierarchically weighted round robin scheme, usingfrequency is uniformly distributed among precalculated paths.

Third Embodiment

A link state routing communication device according to a thirdembodiment of the present invention is designed to be used in a singlepeer group.

Referring to FIG. 8, the link state routing communication device isprovided with a link resource information receiver 1, a data processor12, a memory device 13, a connection request receiver 4, and aconnection setup section 5, wherein circuit blocks similar to thosepreviously described with reference to FIG. 1 are denoted by the samereference numerals and the descriptions thereof will be omittedhereinafter.

The data processor 12 is a program-controlled processor on which thefollowing sections are implemented: link resource information updatesection 21; plural-path precalculation section 22; path searcher 23including precalculated path searcher 231, on-demand path searcher 232,and feasibility check section 233; and blocking rate calculation section26. The memory device 13 includes link resource information memory 31,precalculated path memory 32 including precalculated path topologymemory 321 and precalculated path resource information memory 322, andblocking rate memory 34 including blocking rate threshold memory 341,blocking counter 342, and connection attempt counter 343.

Here, a blocking rate means at least one of link blocking rate and pathblocking rate. A link/path blocking rate is defined as β/α, where α isthe number of times a link/path is calculated as a connection candidateand β is the number of times the link/path does not satisfy connectionquality requirements.

The blocking rate threshold memory 341 stores a threshold of link/pathblocking rate, which indicates the limit of performance deterioration.The blocking counter 342 counts the number of times a link/path has beenblocked. The collection attempt count memory 343 stores a feasibilitycounter for counting the number of times the feasibility check has beenperformed for a link/path and/or a connection attempt counter forcounting the number of times the connection setup operation has beenperformed.

The blocking rate calculation section 26 calculates a link/path blockingrate by dividing the link/path blocking count stored in the blockingcounter 342 by the connection attempt count stored in the connectionattempt count memory 343. Then the blocking rate calculation section 26compares the calculated link/path blocking rate with the thresholdstored in the blocking rate threshold memory 341 to determine whetherthe link/path has been impaired. More specifically, when the calculatedlink/path blocking rate is greater than the blocking rate threshold, itis determined that the communication quality of the link/path isimpaired, and then the plural-path precalculation section 22 performsrecalculation of precalculated paths exclusive of the impairedlink/path.

Operation

Referring to FIG. 9, the steps A1–A3 and A5–A7 are the same as those inFIG. 2 and therefore the details will be omitted.

When a precalculated path candidate satisfying the required connectionquality is found (YES at step A3), it is output to the feasibility checksection 233 and thereby the feasibility check counter stored in theconnection attempt count memory 343 is incremented by one (step D1). Thefeasibility check section 233 checks whether each link/path on the foundpath candidate satisfies the required connection quality by referring tothe stored link resource information in the link resource informationmemory 31 (step C1).

When the found path candidate does not satisfy the required connectionquality (NO at step C1), the blocking counter 343 for the link/path isincremented by one (step D2). Thereafter, the blocking rate calculationsection 26 calculates a link/path blocking rate of the link/path at thetime when the feasibility check is performed. When the calculatedlink/path blocking rate is greater than the blocking rate threshold, itis determined that the quality of the link/path is impaired, and thenthe plural-path precalculation section 22 performs recalculation ofprecalculated paths exclusive of the impaired link/path and updates theprecalculated path information stored in the precalculated path memory32 (step D3).

On the other hand, when all the links included in the found pathcandidate satisfy the required connection quality (YES at step C1) orwhen an on-demand path satisfying the required connection quality isfound (YES at step A6), the found path candidate or the on-demand pathis output to the connection setup section 5 and thereby the connectionattempt counter is incremented by one (step D4). The connection setupsection 5 attempts the connection setup based on the found pathcandidate. At this time, if a link does not satisfy the requiredconnection quality (NO at step D5), the blocking counter 343 for thelink/path is incremented by one (step D2).

In the step D3, recalculation of precalculated paths exclusive of theimpaired link/path may be performed depending on a threshold T, which isobtained byT=Y×R+(1−Y)×S,where R is a blocking rate when the feasibility check is performed and Sis a blocking rate when the connection setup is attempted. In otherwords, T is obtained by linear interpolation from R and S.

As described above, according to the third embodiment, the link blockingrate for each link is calculated and thereby performance deteriorationof a precalculated path can be detected. Therefore, it is possible todetermine which portion is impaired and re-calculate precalculated pathsexclusive of the impaired portion, resulting in selecting aprecalculated path providing a lower blocking rate.

Fourth Embodiment

A link state routing communication device according to a fourthembodiment of the present invention is designed to be used in a singlepeer group.

Referring to FIG. 10, the link state routing communication device isprovided with a link resource information receiver 1, a data processor14, a memory deice 15, a connection request receiver 4, and a connectionsetup section 5, wherein circuit blocks similar to those previouslydescribed with reference to FIG. 1 are denoted by the same referencenumerals and the descriptions thereof will be omitted hereinafter.

The data processor 14 is a program-controlled processor on which thefollowing sections are implemented: link resource information updatesection 21; plural-path precalculation section 22; path searcher 23including precalculated path searcher 231, on-demand path searcher 232,and feasibility check section 231; and link quality check section 28.The memory device 15 includes link resource information memory 31,precalculated path memory 32 including precalculated path topologymemory 321 and precalculated path resource information memory 322, andlink quality threshold memory 35.

The link quality threshold memory 35 stores a link quality thresholdindicating the permissible lowest quality for communication.

The link quality check section 28 compares updated link resourceinformation received from the link resource information update section21 with the link quality threshold stored in the link quality thresholdmemory 35 to determine whether the changed link satisfies thepermissible lowest quality. If there is a link that is lower than thepermissible lowest quality, the plural-path precalculation section 22performs recalculation of precalculated paths exclusive of the impairedlink.

Operation

Referring to FIG. 11, the steps B0–B2 are the same as those in FIG. 5and therefore the details will be omitted.

The link resource information update section 2l identifies a link onwhich a change of resource information occurs and the updated linkresource information is output to the link quality check section 28(step B1).

The link quality check section 28 compares the updated link resourceinformation with the link quality threshold stored in the link qualitythreshold memory 35 (step E1).

When the quality of updated link resource information is lower than thelink quality threshold (NO at step E1), the plural-path precalculationsection 22 performs recalculation of precalculated paths exclusive ofthe impaired link (step E2).

As described above, according to the fourth embodiment, it is possibleto detect an impaired link based on the ling resource informationreceived from the link resource information receiver 1. Therefore, whensuch an impaired link has been detected, precalculated paths exclusiveof the impaired portion can be re-calculated, resulting in selecting aprecalculated path providing a lower blocking rate.

Fifth Embodiment

A border communication device for link state routing according to afifth embodiment of the present invention is designed to be used in amulti-level hierarchical network. Hereinafter, circuit blocks similar tothose previously described with reference to FIGS. 1 and 4 are denotedby the same reference numerals and the details will be omitted.

Referring to FIG. 12, the border communication device is provided with alink resource information receiver 1, a data processor 16, a memorydeice 17, and a summarized information transmitter 8. The link resourceinformation receiver 1 receives link resource information from anothercommunication device and outputs it to the data processor 16. The dataprocessor 16 performs a link state routing operation using the memorydevice 17. The summarized information transmitter 8 transmits summarizedinformation to different-level node under control of the data processor16.

The data processor 16 is a program-controlled processor on which thefollowing sections are implemented: link resource information updatesection 21, plural-path precalculation section 22, and high-speedsummarized information calculation section 62 including precalculatedpath resource information searcher 25 (see FIG. 4) and summarizedinformation calculator 621. The memory device 17 includes link resourceinformation memory 31 and precalculated path memory 32 includingprecalculated path topology memory 321 and precalculated path resourceinformation memory 322.

The summarized information calculator 621 searches the precalculatedpath topology memory 321 and the link resource information memory 31 forpath resource information and calculates summarized information from thefound path resource information. The summarized information is suppliedto the summarized information transmitter 8. The high-speed summarizedinformation calculator 62 can calculate the summarized information basedon the precalculated path information at high speed.

Summarized Link State Information

As shown in FIG. 13A, it is assumed that a hierarchical network iscomposed of four levels 601, 602, 603, and 604. Here, a peer group ofthe level 602 consists of five nodes 501–505, in which nodes 501, 503,and 505 are border nodes connected to different levels 601, 603, and604, respectively.

As shown in FIG. 13B, in the case where the link resource information ofthe level 602 is sent to the different level 601, the link resourceinformation of the level 602 is summarized to produce summarizedinformation 702, which is sent from the border node 501 to the differentlevel 601. The summarized information 702 is obtained by mapping theinformation of the level 602 into a network where the border nodes 503and 505 are directly connected to the border node 501 through twosummarized links. Accordingly, only the link state information of thetwo summarized links is sent from the border node 501 to the level 601.If such summarized information is not used, it is necessary to send linkstate information representing a total of seven links to the level 601.

EXAMPLE

As shown in FIGS. 14A–14E, it is assumed that a peer group of the level602 consists of five nodes 501–505 (see FIG. 14A) and four precalculatedpaths 521–524 from the border node 501 to the border node 503 areconsidered (see FIGS. 14B–14E).

In this case, a link resource information table 511 as shown in FIG. 14Frepresents the link resource information of the level 602 and aprecalculated path information table 531 as shown in FIG. 14G representsthe precalculated paths 521–524 from the border node 501 to the bordernode 503. Referring to FIG. 14F, a link a-b, for example, has a delay of3 msec and an available bandwidth (BW) of 30 Mbps. Referring to FIG.14G, a precalculated path a-b-c, for example, has a delay of 7 msec andan available bandwidth of 80 Mbps.

FIG. 15 shows a summarized information table 591, which is obtained fromthe precalculated path information table 531 and represents a summarizedlink from the border node 7021 to the border node 7023 as shown in FIG.13B.

The precalculated path resource information searcher 25 searches thelink resource information table 511 for resource information of theprecalculated paths 521–524 to produce the precalculated pathinformation table 531.

The summarized information calculator 621 searches the precalculatedpath information table 531 for precalculated path informationappropriate to summarized link information between the border nodes 501and 503.

For example, when the best value is selected from the precalculated pathresource information, the policy best value (delay: 2 msec and availablebandwidth: 80 Mbps) is selected as summarized link resource information(see the table 591 of FIG. 15). When the worst value is selected fromthe precalculated path resource information, the policy worst value(delay: 7 msec and available bandwidth: 3 Mbps) is selected assummarized link resource information (see the table 591 of FIG. 15).

In the case of linear interpolation from the best and worst values, thedelay time and the available bandwidth (BW) are represented by thefollowing expressions:Delay: 2X+7(1−X)[msec]; andAvailable BW: 80X+30(1−X)=30+50X [Mbps],where X is a real number between 0 and 1 (see the table 591 of FIG. 15).

Similarly, the summarized information calculator 621 can determine othersummarized link state information (here, between the border nodes 501and 505).

Since summarized information is calculated using precalculated paths,high-speed processing can be achieved.

Sixth Embodiment

A border communication device according to a sixth embodiment isprovided with a precalculated path memory 33 including a link-pathcorrespondence table 323 as shown in FIG. 4, in place of theprecalculated path memory 32 of FIG. 12.

As described before, the link-path correspondence table 323 indicateswhich of precalculated paths each link is included in.

The precalculated path resource information searcher 25 receives updatelink information from the link resource information update section 21and uses the update link information as a search key to search thelink-path correspondence table 323 for a corresponding precalculatedpath. Thereafter, the precalculated path resource information searcher25 searches the link resource information memory 31 for link resourceinformation of the corresponding precalculated path and, if found, thenupdates the path resource information stored in the precalculated pathresource information memory 322. Accordingly, the link resourceinformation is updated and, at the same time, the path resourceinformation of the corresponding precalculated path is also updated. Inother words, when the link resource information is updated, only thepath resource information of the corresponding precalculated path isre-calculated, resulting in reduced number of computation times andthereby decreased computation load.

Seventh Embodiment

A border communication device for link state routing according to aseventh embodiment of the present invention is designed to be used in amulti-level hierarchical network. Hereinafter, circuit blocks similar tothose previously described with reference to FIG. 1 are denoted by thesame reference numerals and the details will be omitted.

Referring to FIG. 16, the border communication device is provided with alink resource information receiver 1, a data processor 18, a memorydeice 19, and a summarized information transmitter 8. The link resourceinformation receiver 1 receives link resource information from anothercommunication device and outputs it to the data processor 18. The dataprocessor 18 performs a link state routing operation using the memorydevice 19. The summarized information transmitter 8 transmits summarizedinformation to different-level node under control of the data processor18.

The data processor 18 is a program-controlled processor on which thefollowing sections are implemented: link resource information updatesection 21; summarized information calculation section 61; change ratedetector 63; and change rate comparator 64. The memory device 19includes link resource information memory 31, summarized informationmemory 36, and change rate threshold memory 37.

The summarized information memory 36 stores summarized information thatwas previously sent to a different-level node.

The change rate threshold memory 37 stores a change rate threshold whichis used to determine whether summarized information should be sent to adifferent-level node.

The change rate detector 63 compares new summarized information receivedfrom the summarized information calculator 61 with the stored summarizedinformation that was previously sent to a different-level node toproduce a change rate of summarized information. The new summarizedinformation and the calculated change rate are output to the change ratecomparator 64.

The change rate comparator 64 compares the calculated change rate withthe change rate threshold stored in the change rate threshold memory 37to determine whether old summarized information should be replaced withthe new summarized information. More specifically, when the calculatedchange rate is greater than the change rate threshold, the change ratecomparator 64 updates the stored summarized information of thesummarized information memory 36 into the new summarized information andoutputs the new summarized information to the summarized informationtransmitter 8.

Operation

Referring to FIG. 17, when the link resource information update section21 receives link resource information from the link state resourceinformation receiver 1 (step G0), the summarized information calculator61 calculates new summarized information obtained by summarizing networkstatus of nodes in its own level while referring to the contents of thelink resource information memory 31 (step G1). The new summarizedinformation is output to the change rate detector 63.

The change rate detector 63 compares the new summarized information withthe previously summarized information stored in the summarizedinformation memory 36 to produce a change rate of summarized information(step G2). The calculated change rate is output to the change ratecomparator 64.

The change rate comparator 64 compares the calculated change rate withthe change rate threshold stored in the change rate threshold memory 37(step G3). When the calculated change rate is equal to or greater thanthe change rate threshold (YES at step G3), it is determined that alarge amount of change occurs. In this case, the change rate comparator64 updates the stored summarized information in the summarizedinformation memory 36 into the new summarized information (step G4) andoutputs the new summarized information to the summarized informationtransmitter 8 (step G5).

Contrarily, when the calculated change rate is smaller than the changerate threshold (NO at step G3), it is determined that a small amount ofchange occurs and the process is terminated without sending calculatedsummarized information.

EXAMPLE

FIG. 18A shows a table 581 containing link resource information of thelink a-e in the level 602 as shown in FIG. 13A. FIG. 18B shows a table582 containing information of precalculated paths: first precalculatedpath from node 501 to node 503; and second precalculated path from node501 to node 505. Such information of precalculated paths is used tocalculate summarized information of the level 602. FIG. 18C shows atable 583 containing summarized information of the level 602 that iscalculated from the table 582.

It is assumed that the delay time of the link a-e is changed from 1 msecto 3 msec and the available bandwidth thereof is changed from 50 Mbps to20 Mbps.

The summarized information calculator 61 first updates precalculatedpath resource information as shown in the table 582 of FIG. 18B.Thereafter, the summarized information calculator 61 changes summarizedinformation based on the updated precalculated path resource informationas shown in the table 583 of FIG. 18C.

The change rate detector 63 calculates a change rate of summarizedinformation. Here, the following expression is used to calculate achange rate of summarized information:|R _(org) −R _(last) |/R _(last),where R_(org) is a resource value before updated and R_(last) is aresource value after updated.

A change rate of entire summarized information can be obtained, forexample, by summing change rates of all summarized links includedtherein. A change rate of a summarized link can be obtained, forexample, by summing change rates of resource information of respectivelinks to be summarized.

In the case where a policy of selecting a best value is employed, thesummarized link a-c provides a delay change rate of 33% and an availablebandwidth change rate of 0% (see the table 583 of FIG. 18C) andtherefore a total of change rates in the summarized link a-c is33%=33%+0%. Similarly, the summarized link a-d provides a delay changerate of 20% and an available bandwidth change rate of 0% (see the table583 of FIG. 18C) and therefore a total of change rates in the summarizedlink a-c is 20%=20%+0%. Accordingly, a change rate of entire summarizedinformation is 53% which is obtained by summing the calculated changerates of the summarized links, that is, 33%+20%=53%.

On the other hand, in the case where a policy of selecting a worst valueis employed, the summarized link a-c provides a delay change rate of 13%and an available bandwidth change rate of 50% (see the table 583 of FIG.18C) and therefore a total of change rates in the summarized link a-c is63%=13%+50%. Similarly, the summarized link a-d provides a delay changerate of 0% and an available bandwidth change rate of 50% (see the table583 of FIG. 18C) and therefore a total of change rates in the summarizedlink a-c is 50%=0%+50%. Accordingly, a change rate of entire summarizedinformation is 113% which is obtained by summing the calculated changerates of the summarized links, that is, 63%+50%=113%.

As described above, a change rate is calculated by comparing calculatedsummarized information with the stored summarized information that waspreviously sent to the different-level node. Only if a large amount ofchange occurs, that is, the calculated change rate is greater than thethreshold, the summarized information is sent to a different-level node,resulting in reduced amount of summarized information transferred in thenetwork.

1. A link state routing device of a node in a network comprising aplurality of nodes and links, said link state routing device comprising:a first memory for storing link resource information for each link inthe network, wherein the link resource information is updated as anoccasion to do so arises; a path calculator for calculating a pluralityof precalculated paths from a source node to at least one destinationnode based on link resource information stored in the first memory,independently of occurrence of a connection request; a second memory forstoring the precalculated paths and path resource information for eachprecalculated path; a path selector for selecting a precalculated pathfrom the precalculated paths stored in the second memory when aconnection request occurs, wherein the precalculated path is selected soas to satisfy a quality requirement of the connection request; aconnection setup attempter for attempting connection setup of theprecalculated path; a first counter for counting the number of pathselection occurrences in the path selector; a second counter forcounting the number of path blocking occurrences in the connection setupattempter; a blocking rate calculator for calculating a blocking ratebased on the counted number of path selection occurrences and thecounted number of path blocking occurrences; and a controllercontrolling the path calculator such that, when the blocking rate is notsmaller than a predetermined threshold, the path calculator recalculatesa plurality of precalculated paths for each destination node based onlink resource information stored in the first memory.
 2. The link staterouting device according to claim 1, wherein the path selectorcomprises: a precalculated path searcher for searching the second memoryfor a precalculated path candidate satisfying the quality requirement ofthe connection request; and a feasibility checker for checking whetherthe precalculated path candidate comprises a feasible path, by referringto link resource information stored in the first memory, wherein, whenthe precalculated path candidate comprises an infeasible path, theprecalculated path searcher searches the second memory for anotherprecalculated path candidate.
 3. The link state routing device accordingto claim 2, wherein the path selector further comprises: an on-demandpath searcher for searching the first memory for a path candidatesatisfying the quality requirement of the connection request, wherein,when a precalculated path candidate satisfying the quality requirementof the connection request is not found, the on-demand path searcher isactivated.
 4. The link state routing device according to claim 2,wherein the blocking rate calculator calculates a blocking rate based onthe counted number of feasibility check occurrences and the countednumber of path blocking occurrences.
 5. The link state routing deviceaccording to claim 1, further comprising: an updater for updating thepath resource information of a precalculated path stored in the secondmemory when link resource information of a link included in theprecalculated path is updated.
 6. The link state routing deviceaccording to claim 5, wherein the path selector further comprises: anon-demand path searcher for searching the first memory for a pathcandidate satisfying the quality requirement of the connection request,wherein, when a precalculated path candidate satisfying the qualityrequirement of the connection request is not found, the on-demand pathsearcher is activated.
 7. The link state routing device according toclaim 5, further comprising a controller controlling the path calculatorsuch that, when the updated link resource information of the link is notsmaller than a predetermined link quality threshold, the path calculatorrecalculates a plurality of precalculated paths for each destinationnode exclusive of the updated link resource information of the link. 8.The link state routing device according to claim 1, wherein the pathcalculator calculates a plurality of precalculated paths for eachdestination node based on a link-inherent parameter that is independentof link resource information.
 9. The link state routing device accordingto claim 1, wherein the path calculator calculates a precalculated pathbased on a single parameter a plurality of times to produce a pluralityof precalculated paths for each destination node.
 10. The link staterouting device according to claim 1, wherein the path calculatorcalculates a plurality of precalculated paths for each destination nodebased on an integrated parameter set having a plurality of parametersintegrated therein.
 11. The link state routing device according to claim10, wherein the path selector sorts the precalculated paths stored inthe second memory according to the integrated parameter set to searchthe second memory for a precalculated path satisfying the qualityrequirement of the connection request.
 12. The link state routing deviceaccording to claim 11, wherein the path selector searches the secondmemory for a precalculated path satisfying the quality requirement ofthe connection request in a round robin fashion weighted by theintegrated parameter set.
 13. The link state routing device according toclaim 12, wherein the path selector searches the second memory for aprecalculated path satisfying the quality requirement of the connectionrequest in a round robin fashion hierarchically weighted by theintegrated parameter set.
 14. The link state routing device according toclaim 1, wherein the link resource information comprises delayinformation and available bandwidth information.
 15. The link staterouting device according to claim 1, wherein the path selector furthercomprises: an on-demand path searcher for searching the first memory fora path candidate satisfying the quality requirement of the connectionrequest, wherein, when a precalculated path candidate satisfying thequality requirement of the connection request is not found, theon-demand searcher is activated.
 16. A communication method in a linkstate routing device of a node in a network comprising a plurality ofnodes and links, said method comprising: storing link resourceinformation for each link in the network in a first memory; updating thelink resource information as an occasion to do so arises; calculating aplurality of precalculated paths from a source node to at least onedestination node based on link resource information stored in the firstmemory, independently of occurrence of a connection request; storing theprecalculated paths and path resource information for each precalculatedpath in a second memory; selecting a precalculated path from theprecalculated paths stored in the second memory when a connectionrequest occurs, wherein the precalculated path is selected so as tosatisfy a quality requirement of the connection request; attemptingconnection setup of the precalculated path: counting the number of pathselection occurrences in the path selector; counting the number of pathblocking occurrences during the attempting of the connection setup;calculating a blocking rate based on the counted number of pathselection occurrences and the counted number of path blockingoccurrences; and when the blocking rate is not smaller than apredetermined threshold, recalculating a plurality of the precalculatedpaths for each destination node based on link resource informationstored in the first memory.
 17. The method according to claim 16,wherein selecting the precalculated path comprises: searching the secondmemory for a precalculated path candidate satisfying the qualityrequirement of the connection request; and checking whether theprecalculated path candidate comprises a feasible path, by referring tolink resource information stored in the first memory, wherein, when theprecalculated path candidate comprises an infeasible path, the secondmemory is searched for another precalculated path candidate.
 18. Themethod according to claim 16, further comprising: updating the pathresource information of a precalculated path stored in the second memorywhen link resource information of a link included in the precalculatedpath is updated.
 19. The method according to claim 16, furthercomprising: updating path resource information of a precalculated pathstored in the second memory when link resource information of a linkincluded in the precalculated path is updated; and when the update linkresource information of the link is not smaller than a predeterminedlink quality threshold, recalculating a plurality of precalculated pathsfor each destination node exclusive of the updated link resourceinformation of the link.
 20. The method according to claim 16, whereinthe link resource information comprises delay information and availablebandwidth information.